Retrofit with Kotlin Coroutine in Android

Retrofit is a type-safe http client which is used to retrieve, update and delete the data from web services. Nowadays retrofit library is popular among the developers to use the API key. The Kotlin team defines coroutines as “lightweight threads”. They are sort of tasks that the actual threads can execute. Coroutines were added to Kotlin in version 1.3 and are based on established concepts from other languages. Kotlin coroutines introduce a new style of concurrency that can be used on Android to simplify async code. In this article, we will learn about retrofit using Kotlin coroutine. So we will be using Retrofit for network requests. Retrofit is a very popular library used for working APIs and very commonly used as well. We will learn it by making a simple app using an API to get some data using Retrofit.

Step by Step Implementation

Step 1: Create a New Project

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio.

Step 2: Add dependency 

Navigate to the Gradle Scripts > build.gradle(Module:app) and add the below dependency in the dependencies section.

// retrofit

implementation ‘com.squareup.retrofit2:retrofit:2.9.0’

// GSON

implementation ‘com.squareup.retrofit2:converter-gson:2.9.0’

// coroutine

implementation ‘org.jetbrains.kotlinx:kotlinx-coroutines-android:1.5.2’

implementation ‘org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.2’

We are using GSON to convert JSON to kotlin(Java) object. We will add these dependencies in build.gradle file inside our project.

Step 3: We will use the below API

https://quotable.io/quotes?page=1

Figure 01

So our JSON response will look like this Figure01.

Step 4: Then we will create data classes according to JSON response

In JSON response we have 2 JSON objects, So we will create 2 data class 

1. QuoteList
2. Results

Kotlin

// data class QuoteList
// according to JSON response
package com.ayush.retrofitexample

data class QuoteList(
    val count: Int,
    val lastItemIndex: Int,
    val page: Int,
    val results: List<Result>,
    val totalCount: Int,
    val totalPages: Int
)

2nd data class

Kotlin

package com.ayush.retrofitexample

data class Result(
    val _id: String,
    val author: String,
    val authorSlug: String,
    val content: String,
    val dateAdded: String,
    val dateModified: String,
    val length: Int,
    val tags: List<String>
)

Step 5: We will create a Retrofit interface to add the endpoints of the URL (quotes in our case is the endpoint)

Kotlin

// Retrofit interface
package com.ayush.retrofitexample

import retrofit2.Response
import retrofit2.http.GET
import retrofit2.http.Query

interface QuotesApi {
    @GET("/quotes")
    suspend fun getQuotes() : Response<QuoteList>
}

Step 6: We will create a new file to get the Retrofit object

In this file, we will have a function that will return the Retrofit object.

Kotlin

package com.ayush.retrofitexample

import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory

object RetrofitHelper {

    val baseUrl = "https://quotable.io/"

    fun getInstance(): Retrofit {
        return Retrofit.Builder().baseUrl(baseUrl)
            .addConverterFactory(GsonConverterFactory.create())
            // we need to add converter factory to
            // convert JSON object to Java object
            .build()
    }
}

Step 7: Now we will link the Retrofit object and Retrofit interface file in MainActivity

Kotlin

package com.ayush.retrofitexample

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.launch
import retrofit2.create

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val quotesApi = RetrofitHelper.getInstance().create(QuotesApi::class.java)
        // launching a new coroutine
        GlobalScope.launch {
          val result = quotesApi.getQuotes()
            if (result != null)
                // Checking the results
                Log.d("ayush: ", result.body().toString())
        }

    }
}

Step 8: Add Internet permission in the manifests file

<uses-permission android:name=”android.permission.INTERNET”></uses-permission>

Results: we can check the logcat window. We can see the result in the green box.

Output: